1. Field of the Invention
The present invention relates to methods and databases for identifying nuclides.
2. Description of the Related Art
In prior art, for radiation detection, various gamma spectroscopic devices are known, as for example, digital gamma spectrometers which allow a user to locate a radioactive or nuclear source, and, once found, to identify the isotope or isotope thus detected.
Such radiation detectors are employed—amongst others—for aviation security, border security, and facility security. Especially in view of modern defense strategies against nuclear terrorism, gamma spectroscopic surveillance of vital infrastructure has become a cornerstone. Facing an increasingly globalized world, illicit traffic of special nuclear materials is an urgent threat to our societies. As a matter of fact, sensitive locations are secured by applying two complementary detector types regarding to radiation: (a) stationary portals and (b) handheld instruments.
In devices known from prior art, both types acquire spectra and are thus principally capable of identifying the nuclides that contribute to the radiation wherein for nuclide identification, two concepts are known: peak search and template matching. The central objective of devices that apply nuclide identification is to correctly identify all sources in sight of the device. Threat materials denoted as special nuclear material (SNM), e.g., Uranium or Plutonium, are high priority sources that should be found in any circumstances.
A prototypical difficulty in such surveillance scenarios are travelling radiologic patients. Due to their treatment, those people are contaminated with high doses of short living isotopes, like Tc-99m or I-131, but should in general not be regarded as a threat. Consequently, the results of nuclide identification algorithms are mapped by a threat decision, that designates which nuclide is regarded as innocent or threat. In a special sense, these patients are challenging for nuclide identification algorithms, since most of the source is distributed throughout human tissue, and the radiation is heavily scattered.
This scattering distortion leads to various problems. First of all, as mentioned above, nuclides are not identified correctly, as peaks are missing or have low intensity. Secondly, masked nuclides, especially SNM, are not identified correctly due to scattering; and, also, the confidences for the found nuclides are not correct. Evidently, these problems have a direct effect on the performance with SNM.
Additionally, a new question arises with the medical sources that are initially assumed to be innocuous: Is the medical source contained in a human body or not? If the source is not inside the human body, the medical material is very likely to be shipped illegally.
Known gamma spectroscopic devices which are employed, for example, for homeland security applications and which are implemented as handheld instruments as well as portal concepts have a threat mapping for assorted nuclides, as outlined above. They deploy a nuclide identification algorithm and propagate its result to the user.
However, current technologies do not consider the above mentioned scattering caused, for example, by human body tissue and, in principle, cannot uncover sources that are masked by the scattering trace. Further, known nuclide identification algorithms principally do not consider absorption corrections either so that these algorithms are not capable of predicting the amount of attenuation. This, in turn, leads to incorrect results, and, thus, to high security vulnerability.